1. Field of the Invention
The invention relates to fuel supply installation of an aircraft turbojet and more particularly relates to a refinement for optimising components, especially in terms of weight and bulk, while reducing mechanical and thermal losses resulting from recirculation of excess fuel at different operating rates of the turbojet.
2. Description of the Related Art
In an aircraft turbojet, the main high-pressure pump supplying fuel to the combustion chamber is of volumetric type, for example a gear pump. This type of pump has a linear flow characteristic as a function of the speed at which it is driven. The pump is conventionally dimensioned so that said flow characteristic can satisfy all operating rates. The crucial point is the flow rate necessary on ignition. This dimensioning point therefore determines a linear characteristic of relatively high given slope such that the curve representative of the fuel flow rate as a function of the operating rate of the turbojet is at any point below the straight line passing through this dimensioning point.
It eventuates that the pump must be able to ensure a relatively substantial flow rate (the pump is therefore heavier and bulkier than necessary) and that it is imperative to permanently recycle a considerable quantity of fuel, at any operating rate of the turbojet. The result is a drop in excess mechanical power on the gearbox of the turbojet and thermal losses due to recirculation of excess fuel.
U.S. Pat. No. 5,110,269 describes a system using a double pump, driven mechanically. According to the operating rate of the motor, the flow rate of one of the stages of the double pump can be restarted and recycled. This solution does not allow for the preferred optimisation.